Cathode-ray tube comprising a luminescent screen



Nov. 13, 1956 A. BRIL ET AL 2,770,749

CATHODE-RAY TUBE COMPRISING A LUMINESCEINT SCREEN Filed Oct. 50, 1952 2Sheets-Sheet l INVENTORS ALF-RED BRILL HENDRIK ANNE KLASENS PIETER ZALMAGENT Nov. 13, 1956 A. BRIL ET AL 2,770,749

OATHODE-RAY TUBE COMPRISING A LUMINESCENT SCREEN Filed Oct. 30, 1952 2Sheets-Sheet 2 m Fig. 2

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\ INVENTORS Alfred Bril Hendrik Anne Klosens BY Pieter Zulm AGENT UnitedStates Patent CATHODE-RAY TUBE COMPRISING A LUMINESCENT SCREEN AlfredBril, Hendrik A. Klasens, and Pieter Zalm, Eindhoven, Netherlands,assignors to Hartford National Bank and Trust Company, Hartford, Conn,as trustee Application October 30, 1952, Serial No. 317,716

Claims priority, application Netherlands August 21, 1952 1 Claim. (Cl.313-92) This invention relates to a cathode-ray tube comprising aluminescent screen, of which the decay time is shorter than 10" sec. Theinvention furthermore relates to an apparatus for converting radiationpulses into electrical pulses, which comprises such a cathode-ray tube.

In cathode-ray tubes comprising a luminescent screen, it is in certaincases desirable that the luminescent material should exhibit aluminescence having a decay time shorter than sec. The term decay-timeof the luminescence is to be understood here to mean the time in whichthe intensity of the emitted radiation, after the excitation has ceased,decreases to l/e of its maximum value. Such a case occurs, for example,when a cathoderay tube is used as a source of radiation in apparatus forconverting radiation pulses into electrical pulses. One of therepresentatives of this kind of apparatus which is most known is theflying spot scanner which is used inter alia for the transmission oftelevision images of films or lantern slides. In flying-spot scannersthe cathode-ray describes on the screen of the cathode-ray tube a framewhich serves as a source of rays for lighting the image of the film orthe lantern slide. The radiation traversing the image is received by aphoto-electric cell and converted thereby into electrical pulses.

The wavelength corresponding to the maximum of the spectral distributionof the emitted radiation is comprised between 3800 A. and 5500 A. formost cathode-ray tubes used for this purpose. A luminescent substancewhich is frequently used is, for example, green-luminescent zincoxidewhich has a decay-time of about 10- sec. The use of silicates of thealikaline-earth metals or alkaline metals, activated with trivalentcerium, is also known in this connection.

For uses other than for a flying-spot scanner, it may also be importantto dispose of a cathode-ray tube having a luminescent screen with adecay time shorter than 10- sec. As examples thereof may be mentionedradar and fascimile transmission.

Our invention will be more apparent after referring to the followingspecification and attached drawing in which:

Figure 1 is a view partially in perspective and partially in section ofa cathode-ray tube manufactured according to our invention; and

Figure 2 is a graph showing the relationship of the wavelength of theradiation emitted by the luminescent material of our invention to theintensity of the emitted radiation.

A cathode-ray tube according to the invention comprises a luminescentscreen having a decay time shorter than 10- sec. and is characterized bythe fact that the luminescent screen contains ultra-violet-luminescentzirconium pyrophosphate and that the window consists of material whichallows the passage of radiation emitted by zirconium pyrophosphate.

The zirconium pyrophosphate, upon being excited by Patented Nov. 13,1956 electrons, emits a radiation, of which the spectral distributionexhibits a maximum at about 2900 A.

Quartz, for example, may be used as a window for the passage of suchshort-wave ultraviolet radiation.

The energy output of zirconium pyrophosphate upon excitation byelectrons of 20 kilovolts is comparatively high, viz. 4%.

Owing to the ultra-short radiation, a cathode-ray tube according to theinvention may advantageously be utilised for some particular uses forwhich the conventional cathode-ray tubes comprising a luminescent screenhaving a decay time shorter than 10 sec. cannot be employed. Thus, atube according to the invention may be used, for example, as a source ofradiation for measuring the decay time of luminescent substances whichare required to be excited by short-wave ultraviolet radiation, since itis extremely simple to obtain rapidly extinguishing radiation pulsesfrom such a cathode-ray tube by supplying a suitable voltage, forexample a so-called block voltage, to the electrode controlling theintensity of the cathode-ray. The use of a cathode-ray tube according tothe invention is furthermore of particular importance in devices inwhich the radiation from the luminescent screen traverses a microscopein a direction which is inverse to the ordinary path of the light raysin a microscope, that is to say through the ocular, then through theobjective and finally through the object. Such devices are already knownfor use with visible light. In such devices, a greatly reduced image ofthe raster appearing on the screen of the cathode-ray tube is reproducedon the object and the light transmitted by the object is received by aphotoelectric cell and converted into electrical pulses, which mayserve, if desired after being amplified, to produce an image identicalwith the object on the screen of a cathode-ray tube. It is evident,that, as an alternative, the electrical pulses may be transmitted via atransmitter and received at far distant places to be used in acathode-ray tube for the composition of an image. Since, as iswell-known, a greater resolving power is obtained if ultravioletradiation and preferably shortwave ultraviolet radiation instead oflight is used, it is evident that a cathode-ray tube according to theinvention is very important for such a use, since it emits radiationwith a maximum at about 2900 A. Furthermore, it is possible to makevisible objects which absorb solely ultraviolet radiation. In such adevice the microscope is naturally required to comprise lenses whichallow the passage of ultraviolet rays and hence consist, for example, ofquartz.

The zirconium pyrophosphate used in a cathode-ray tube according to theinvention is self-activated, i. e., unactivated, and may be manufacturedin the following manner.

Example One prepares a mixture of:

26.5 gs. of (NH4)2HPO4 32.2 gs. of ZrOClz-SHzO in 0.1 litre of water.This suspension is dried by vaporisation and the dry substance is heatedin air at about 400 C. for 1% hours. The resultant product is groundand, if necessary, sieved, whereafter renewed heating in air follows at1050 C. for about 4 hours. The substance obtained after this heating isground, if desired sieved, and heated in air at about 1000 C. for about2 hours. Finally, the substance is prepared for use by grinding andsieving.

Instead of utilising the above-mentioned zirconium oxychloride, use maybe made of an equivalent amount of an other zirconium compound, forexample zirconium oxide.

' example deposited on the inside of quartz Window 4.

Figure 2 in the drawing shows a curve in which the wavelength of theradiation emitted by zirconium pyrophosphate manufactured in accordancewith the preceding example upon excitation by electrons of 20 kilovoltsand the intensity of the emitted radiation in arbitrary units areplotted on the axis of abscissae and the axis of ordinates respectively.

What we claim is:

In a cathode-ray tube with a decay time shorter than 10- seconds andemitting ultra-violet radiation, the spectral distribution of whichexhibits a maximum at about 2900 A., including an envelope having aquartz Window at one end and means for producing a beam of electrons 43.within said tube, a luminescent screen consisting of selfactivatedzirconium pyrophosphate.

References Cited in the file of this patent UNITED STATES PATENTS2,225,044 George Dec. 17, 1940 2,450,548 Gisolf et a1. Oct. 5, 19482,455,415 Froelich Dec. 7, 1948 2,488,733 McKeag et al Nov. 22, 19492,521,571 DuMont et a1. Sept. 5, 1950 2,596,509 Ranby May 13, 1952FOREIGN PATENTS 311,282 Great Britain Aug. 7, 1930 OTHER REFERENCES SomeAspects of the Luminescence of Solids by F. A. Kroger 1948, pages159-161.

